The present invention relates to a magnetic recording medium having a magnetic layer obtained by applying a magnetic paint (magnetic coating materials) containing a ferromagnetic powder used for recording and reproducing images, voices and data.
Previously, some magnetic recording media have been known which have magnetic layers formed by applying magnetic paints comprising magnetic powders and binders to non-magnetic supports, said binders being combinations of a plurality of resins.
For example, magnetic recording media have been known such as "a magnetic recording medium comprising a non-magnetic support and a magnetic layer formed thereon comprising a ferromagnetic metal powder and a binder, wherein said binder comprises three kinds of binder resins different from one another in glass transition temperature (Tg), and a mixed resin composition of these three kinds of resins has a glass transition temperature (Tg) of 30.degree. C. to 47.degree. C." (Japanese Patent Unexamined Publication No. 3-286419), "a magnetic recording medium comprising a non-magnetic support and a magnetic layer formed thereon comprising a ferromagnetic powder and a binder, wherein said binder consists of at least two kinds of polyester-polyurethane resins different from each other in glass transition temperature, and has a glass transition temperature of 10.degree. C. to 60.degree. C. as a whole" (Japanese Patent Unexamined Publication No. 5-307734), and "a magnetic recording medium comprising a non-magnetic support and a magnetic layer formed thereon comprising a ferromagnetic powder and carbon black dispersed in a binder, wherein said binder contains a copolymer having amine-modified vinyl units and acidic functional group-containing vinyl units, and said carbon black has a specific surface area of 90 m.sup.2 /g to 330 m.sup.2 /g and a DBP oil absorption of 45 ml/100 g to 120 ml/100 g" (Japanese Patent Unexamined Publication No. 7-153055).
Japanese Patent Unexamined Publication No. 3-286419 described above discloses that the three kinds of resins different from one another in glass transition temperature are used as the binder, thereby obtaining the magnetic recording medium excellent in surface properties and mechanical strength and improved in durability. Further, Japanese Patent Unexamined Publication No. 5-307734 discloses that at least two kinds of polyester-polyurethane resins different from each other in glass transition temperature are used as the binder, thereby resulting an improvement in electromagnetic characteristics. However, both of them do not describe vinyl chloride copolymers in detail, and have a problem with respect to the dispersibility of paints. Japanese Patent Unexamined Publication No. 7-153055 is directed to the use of the copolymer having amine-modified vinyl units and acidic functional group-containing vinyl units in a molecule as the binder, which provides the magnetic recording medium excellent in dispersibility. However, it is silent on the use of two kinds of polyurethane resins.
For conventional techniques, problems are left unsolved with regard to the dispersibility and the dispersion stability of the magnetic paints. As a result, the electromagnetic characteristics are deteriorated, resulting in a problem with respect to running durability. It has been therefore desired to provide a magnetic recording medium excellent in both the electromagnetic characteristics and the running durability.